Actor Casey Affleck is known to most celebrity-watchers as Ben Affleck's younger brother and sometime co-star. But after a decade of working in the movies, Casey Affleck emerged in 2007 as a lead player, seen alongside Brad Pitt in The Assassination of Jesse James by the Coward Robert Ford and starring with Ed Harris in his brother's directorial debut, Gone, Baby, Gone (with Amy Ryan). He first appeared with Joaquin Phoenix as an aimless teen in Gus Van Sant's To Die For (1995). He had small but memorable roles in Good Will Hunting (1997) and American Pie (1999), then played sort-of leads in the poorly-received movies Drowning Mona (2000) and Soul Survivors (2001). He gained a wider audience as part of the gang in Steven Soderbergh's series of Ocean's Eleven movies (2001-07), and has since moved into starring roles, including the 2002 artsy Van Sant movie Gerry (which Casey co-wrote with Matt Damon), the Steve Buscemi film Lonesome Jim (2005) and the independent thriller The Killer Inside Me (2010). He began filming Joaquin Phoenix (his brother-in-law) in 2008, just as Phoenix announced his "retirement" as an actor. The resulting documentary film, 2010's I'm Still Here, was described by Affleck as "performance art" rather than hoax.

Casey Affleck is a vegan and promotes the humane treatment of animals... He is married to Summer Phoenix, sister of Joaquin and River, and they have two children.